Process and apparatus for digesting fibrous material



H. GEVERS.

PROCESS AND APPARATUS FOR DIGESTING FIBROUS MATERIAL.

APPLICATION FILED APR.24. 1920.

1,385,744; Patented July 26, 1921.

UNITED STATES PATENT OFFICE.

'HERMANN GEVERS, OF KAUKAUNA, WISCONSIN.

PROOIESS AND APPARATUS FOR DIGESTING FIBROUS MATERIAL.

Specification of Letters Patent.

Patented July 26, 1921.

Application filed April 24, 1920. Serial No. 376,371".

equipment required and render the process more rapid and economical, and the invention consists in the features hereinafter set forth and more particularly pointed out in the appended claims.

Heretofore, in manufacturing cellulose by the soda or sulfate process, the charge of fibrous material and liquor in the digester has usually been heated either by. directly injecting steam or by the so-called indlrect method, in which the liquor is circulated through a steam heater and in which the steam does not come in contact with the digestion liquor. In the indirect method, an injector or centrifugal pump is usually employed to circulate the liquor from the bottom to the top of the digester through the heater. Similar means is at times provided for circulating the liquor in the direct cooking method. The direct injection of steam in the soda or sulfate process is objectionable, since the condensed steam dilutes the liquor. This objection is avoided by the indirect method referred to but in this case the heat of the steam is not as efficiently utilized.

In carrying out the present process, digestion liquor is heated in a boiler which, in accordance with the referred embodiment of the invention, is direct fired so that the use of a boiler for generating steam from water is dispensed with. The liquor is pumped or otherwise forced under pressure into the boiler, is heated therein to generate steam and is brought to a suitable high temperature and pressure, which may be varied in accordance with the different materials to be treated and the size of the ap aratus employed.

11 carrying out a digesting operation, a charge of fresh wood chips or other fibrous material and part of the liquor required for the digesting or cooking operation is placed in the cooking vessel or digester and the latter 1s then closed. The rest of the liquor required for the operation, which has been preheated in the boiler, is then introduced into the digester and, most conveniently, is forced from the boiler by the steam generated therein through a suitable pipe line extending from the boiler at a point below its water level and connected to the digester. Preferably, the pipe line is provided with connections and valves whereby the preheated liquor from the boiler can be admitted either to the top or bottom of the digester, or part into the top and part into the bottom as may be required. When the digester is thus charged, the steam generated from the digestion liquor in the boiler is introduced into the digester and preferably-as is customary with the direct cooking method referred to-means are provided whereby the steam can be introduced either into the upper or the lower end of the digester as conditions may require. During the'cooking and digestion operation, fresh liquor is pumped into the boiler preferably as soon as the digester charge has, by the introduction of preheated liquor and steam,

been brought to the temperature and pressure required for the completion of the cooking operation. The cooking of the digester charge is then continued and completed by aid of steam generated in the boiler and at the same time the boiler is utilized to preheat the liquor for the subsequent operation or operations.

The accompanying drawing is a diagrammatic illustration of an improved apparatus for carrying out the described process. The digester can be of any usual or suitable type.

'In the form shown, it consists of a stationary upright vessel 1 having conical portions 2 and 3 at its upper and lower ends. The upper conical portion 2 is provided with the usual charging opening having a cover plate 4. An elevated storage tank 5 for digestion liquor is in communication with the upper end of the digester through pipe connections 6 controlled by a valve 7. A relief or vent pipe 8 with a valve 9 therein is connected to the upper end of the digesting vessel and a discharge or blow-off pipe 10 having a valve 11 is connected to the bottom of the lower cone 3.

The direct fire boiler for preheating the digester liquor may be of any suitable type. The form shown is a vertical liquid tube boiler comprising upper and lower drums 12 and 13 connected by tubes 14, and a suitable fire box and flues are provided for heating the liquid in the tubes. In the form shown, a blow-off pipe 15 havinga valve 16 therein is connected to the lower drum 13. The upper drum 12 is of considerable height and is provided with a series of overlapping gage glasses 17 for indicating the liquid level therein. Also, as shown, the upper portion of the drum 12 is provided with a pressure gage 18 and a safety valve 19. A boiler feed pump 20 is arranged to draw digestion liquor from a suitable storage tank 21 through a pipe 22 and force it through a pipe 23 into the lower drum 13 of the boiler. The pipes 22 and 23 are provided'with suitable valves 24 and 25 and preferably, also, awater supply pipe 26 with a controlling valve 27 therein is connected to the inlet pipe 22 of the pump. 4

Separate pipe lines 28 and 29 are connected to the upper and lower portions respectively of the upper drum 12 of the boiler, the pipe 28 being employed to supply steam to the digester and the pipe 29 to supply liquor thereto. The steam and liquor supply pipes 28 and 29 are preferably provided adjacent the boiler with controlling valves 30 and non-return check valves 31. The steam pipe 28 is conveniently connected to the relief or vent pipe 8 which communicates with the upper end of the digester and, adjacent the relief pipe, the steam pipe is provided with a valve '32. The steam pipe is also connected to a pipe 33 which communicates with the bottom of the lower con? 3 of the digester, which pipe is provided with controlling valves 34 and 35 adjacent its ends. The pipe 33 also communicates with the side of the lower cone 3 through a pipe 36 and the latter is also connected to the liquid supply pipe 29 and is provided with controlling valves 37 and 38 on opposite sides of its point of connection with the pipe 29. The latter has a controlling valve 39 adjacent the pipe 36.

In carrying out the improved process, the boiler is charged with liquor to its high level (indicated by the dotted line a), is heated to generate steam and bring the liquor to a suitable high temperature and pressure' The pressure in the boiler is preferably brought to about one hundred pounds per square inch (corresponding to a temperature of about 170 C.). However, the pressure may vary from seventy five to one hundred thirty pounds per square inch to meet varying conditions. A charge of fresh wood chips is placed in the cooking vessel 1, part of the digestion liquor is run into the vessel from the tank 5 and the digester cover is then closed. Preferably, the liquor placed in the digester before closing it is about onehalf or two-thirds of the amount required to end of the digester, or into the side of the lower cone 3. Preferably, at the beginning of the operation, some liquor is admitted by opening the valves 39, 38, 34 and 32 into the upper end of the digester to moisten the chips therein and which are not at this time submerged in the liquor. Thereafter, the liquor is preferably introduced either by way of the valve 37 or by way of the valves 38 and 35 into the lower portion of the digester so that it passes upwardly through the digester charge and prevents the packing of the fibrous material in the bottom of the digester. When the cooking vessel is thus suitably charged with digestion liquor, the

and completed in the vessel by introducing steam from the boiler through the pipe line 28. Obviously, by manipulating the different controlling valves, the steam can be admitted either into the top or bottom of the digester or into the side of the lower cone 3 as conditions may require.

When the digester is charged with preheated liquor, the level in the boiler is low ered, say from its high to its low limit, which are indicatedb the dotted lines a and b in the drawing. t some time during the cooking operation and preferably when the charge in the digester has been brought to the required temperature and pressure, fresh liquor is pumped into the boiler to bring the liquid level therein back to its upper limit. Steam for continuing and completing the cooking in the digester is then obtained from the preheating of the liquor for a subsequent operation or operations.

The improved process and apparatus avoid the necessity of employing a water fed boiler to supply steam for heating the digestion liquor. As the preheated liquor is forced from the boiler into the lower portion of the digester and also during the continued cooking operation, gas and vapor are relieved through the pipe 8. This venting of the digester concentrates the liquor. Furthermore, the generation of'steam from the liquor in the boiler also concentrates the liquor so that undue dilution and waste of heat are avoided.

Again, because of the fact that the liquor is concentrated in the boiler, the liquor when first prepared can be weaker than would otherwise be the case The proportion of a weaker cooking liquor is, of course, easier and more economical. A comparatively small amount of lime will furnish the desired causticity. Furthermore, the liquor in the digester can be kept at such a concentration that expensive steam evaporators cooking or digesting portion is continued and extra fuel are not required for the recovery of the alkali from the resulting black liquor. The introduction of highly preheated liquor into the freshly charged digester reduces the cooking time; the boiler is fully utilized not only to supply steam for the cooking operation, but also to preheat the liquor for the succeeding operation; no pump is required for circulating the liquid, which can be forced into different portions of the digester as required by pressure developed in the boiler; and good boiling and circulation during the cooking operation can be readily'attained by venting the digester and by admitting steam to different portions thereof. Again, no heater other than the direct-fire boiler is required.

Obviously, changes may be made in the details set forth without departure from the essentials of the invention as defined in the claims.

I claim as my invention:

1. The process of digesting fibrous material for the manufacture of cellulose, which consists in preheating digestion liquor, introducing the same into a digester charged with fresh material, and continuing the digestion operation with steam developed by preheating the liquor for a subsequent operation.

2. The process of digesting fibrous material, Which consists in preheating digestion liquor to a suitable temperature and pressure, introducing the preheated liquor into a digester charged with fresh material, and

continuing and finishing the digestion operation by introducing into the digester steam developed by the preheating of digestion liquor for a subsequent operation.

3. The process of digesting fibrous material for the manufacture of cellulose, which consists in preheating digestion liquor in a direct-fired boiler, introducing the same into a digester charged with fresh material and continuing the digestion operation with steam from the boiler.

4. The process of digesting fibrous material, which consists in preheating and concentrating digestion liquor in a direct-fired boiler, introducing the preheated liquor into a digester charged with fresh material, and continuing and finishing the operation by introducing into the digester steam developedin the boiler by ,the preheating of digestion liquor for a subsequent operation.

5. The process of digesting fibrous material for the manufacture of cellulose, which consists in inclosing a charge of material in a digester, introducing preheated digestion liquor into the charge, and continuing the 4 operation by introducing into the charge steam developed by the preheating of digestion liquor for a subsequent charge.

6. The process of digesting fibrous material for the manufacture of cellulose, which portion of preheated liquor into the diges- I ter, and continuing the operation with steam developed by the preheating of digestion liquor for a subsequent operation.

8. The process of digesting fibrous material which consists in inclosing a charge of fresh material and a portion of the required liquor in a digester, introducing into the closed digester the remaining portion of liquor preheated to a suitable temperature .and pressure by direct firing, and continuing and finishing the operation by introducing into the digester steam developed by similarly preheating liquor for a subsequent operation.

9. The process of digesting fibrous material, which consists in preheating digestion liquor in a boiler, forcing the liquor by the pressure of steam developed in the boiler into a digester charged with fresh material, and continuing and finishing the operation by introducing steam from the boiler into the di ester.

10. The process of digesting fibrous material, which consists in preheating digestion liquor by direct firing to bring the same to a suitable pressure and temperature, forcing the preheated liquor by the pressure thus developed into an inclosed charge of fibrous material, and continuing and completing the digestion of the charge of material by introducing into the same steam developed by the similar preheat-ing of liquor for a subsequent operation.

11. The process of digesting fibrous material for the manufacture of cellulose, which consists in inclosing acharge of fresh material and a portion of the required liquor in a digester. preheating and concentrating liquor in a direct fired boiler, forcing the remaining portion of liquor required for the operation from the boiler into the digester by the steam pressure developed in the boiler, and continuing and finishing the operation by introducing into the digester steam developed by the similar preheating of liquor for a subsequent operation.

12. An apparatus for digesting fibrous material comprising a direct fired boiler for preheating digestion liquor to a suitable temperature and pressure, a digester, and separate pipe lines through which liquor and steam can be forced by the pressure in said preheating digestion separate pipe lines boiler from said boiler into the lower end of said digester.

13. An apparatus material comprising a for digesting fibrous direct fired boiler for liquor to a suitable temperature and pressure, a digester, and through which liquor and steam! can be forced by the pressure in said boiler from said boiler into said digester, said pipe lines having valves and connections for delivering steam and liquor either into the upper or lower ends of the digester as required.

14. An apparatus for digesting fibrous material comprising a digester, a directfired boiler for preheating the digestion liquor to a suitable temperature and pressure, means for forcing liquor into said boiler, separate pipe lines through which liquor and steam can be forced from said boiler by the pressure therein into the lower HERMANN GEVERS. 

